Motor controlling device

ABSTRACT

A motor-controlling device in which a driving circuit for a motor connected with an AC power supply is controlled through the contacts of a first relay, and positions where a load driven by the motor stops are detected by a position-detecting means. Output signals of the position-detecting means are used to control the motor-driving circuit. Other operating systems are operated through second and third relays while the motor is in operation.

United States Patent Kuniaki et al.

154] MOTOR CONTROLLING DEVICE [72] Inventors: Kubokura Kuniaki; Iwao Sugiyama, both of Hitachi, Japan [73] Assignees Hitachi, Ltd., Chiyoda-ku, Tokyo, Japan [22] Filed: Feb. 9, 1971 [21] Appl. No.: 113,946

[451 Apr. 25, 1972 Primary Examiner-Benjamin Dobeck Attorney-Craig, Antonelli & Hill [30] Foreign Application Priority Data [57] ABSTRACT Feb. 12, 1970 Japan ..4'5/ 12191 A o o t ol ng dev ce in which a driving circuit for a motor connected with an AC power supply is controlled 52 us. Cl ..318/467,318/470, 112/219 through the contacts of a first relay, and Positions where a 5g 5/00 load driven by the motor stops are detected by a position-de- Field of Search ..3 18/466, 467, 470, 282; s means- Output Signals 0f the Positimdetwing means 1 12/219 are used to control the motor-driving circuit. Other operating systems are operated through second and third relays while the motor is in operation.

11 Claims, 14 Drawing Figures MAIN MOTOR 1 33 35 -34 I LOAD 32 BRAKE CLUTCH 36 r I sue MOTOR -1 f r CONTROL DETECTING CF MEANS MEANS CHANGER 1 SUB BRAKE FIG. I

, 3| FIG. 2 I MAIN MOTOR 33 -34 [35 LOAD 32 W CLUTCH -36 SUB MOTOR 4O CONTROL DETECTING MEANs ME CHANGER sue BRAKE H li RL INVENTORS KuJM -Hu KUEBOK H Iw no SbkGPlHMR BY Qhci W, W k R'du;

ATTORNEYs Patented April 25, 1972 lo Sheets-Sheet 2 INVENTORS kumuam Ruse KuRR BY QM,W mklm ATTORNEYS Patented April 25, 1972 10 Sheets-Sheet 3 FIG. 4

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INVENTOR$ KULNIHKI KugOKQRH Iwqo SuGWHMH BYtml RM; ,M a MA L ATTORNEYS Patented April 25, 1972 10 Sheets-Sheet 6 INVENTORS Rumm m Ruao kuuza Iw Ho Bucw IQ I BYCAWgH'MML, $6M k -XAIML ATTORNEYS Patented April 25, 1912 3,659,172

10 Sheets-Sheet 7 FIG. 9

INVENTORS Rummu KuEomARH Iw HO sued YHMFI Patented April 25, 1972 10 Sheets-Sheet 8 J =1 8. K L Q Am. Am E h m m N w Ems w .5 m mmm &. "Ln: M 19 u O 0 m m w mm om mm n N9 m A 5 0m vw ow o 5m mm 4w mm m mm M mm; m. i. s V B78 w mm mm INVENTORS KUNIH l-U K 5 KURR ATTORNEYS Patented April 25, 1972 3,659,172

10 Sheets-Sheet 9 INVENTORS Rumm-u xusoauzfi W IO suru QM l BY CNLSFAMDLM -QXJU2 ATTORNEYS Patented A ril 25, 1972 3,659,172'

10 Sheets-Sheet 10 F .l 6. I3 I POWER OF JFORWARD DEPRESSION 1 I 8 Q 5% $5 DEL X BACKWARD 11 FORWARD DEPRESSION) III DEPRESSION STROKE- N Y Z POWER OF- BACKWARD DEPRESSION F l G I4 23 g O hl INVENTOR Rummu KUBOKURH twao fimsw HMH BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for motors.

2. Description of the Prior Art In recent years, a variety of control devices for industrial sewing machines have been developed in which a needle is adtomatically stopped in position for an improved operating efficiency. Some of these kinds of control devices have, forexample, a main driving motor, auxiliary motor and braking means, with a clutch mechanism interposed between them and a driving shaft of a sewing machine, so that a coupled state is mechanically switched. A control system for such devices is adapted to detect a position of a sewing needle to energize, say, an electromagnetic means. Most of these devices employ a mechanically-operated electrical switch and therefore cannot stand frequent use. Further, because of the inaccuracy in stopping the needle in position, requirements for multiple control of a material-holding device, a thread-cutting device and the like including the timing of stopping the needle lead to the lack of smooth operations and the difficulty of controlling. In addition, the resulting complication of the operating system calls for a high skill for operation.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a multi-purpose control device which performs a variety of control operations with great accuracy by means of a simple mechanism.

Another object of the present invention is to operate safely and accurately a position-detecting means which an operator is liable to contact, and to eliminate a delay time due to 'a relay or the like by operating other control mechanisms simultaneously with the detection of a regular position, thereby improving the operating efficiency and workability.

Still another object of the present invention is to provide a simple electrical holding function and simplify the control of v an auxiliary motor by adding a relay system and auxiliary switch system.

Still another object of the present invention is to control the operation of a mechanically-operated system through a position-detecting means and to improve the safety of. such a means in order to prevent the damage to the device due to erroneous operations.

Still another object of the present invention is to provide a most effective means for preventing, through a mechanical system, damage to machines and equipment due to an operators mishandling of the control device which requires complicated operations, thereby to improve the. safety of the device.

The device according to the present invention is so constructed that the position of a rotational angle ofa load shaft is detected, and the detected signals are used to stop the load shaft at the first position, the control system beingmade ready for operation while transferring from the first to second stop position.

An example of the device according to the present invention comprises a position-detecting means including a switch which operates at the first position of a load driven by a motor and another switch which operates at the second position thereof, a first control element which is energized through a starting switch closed to start a job and which closes a driving circuit of the motor while the above-mentioned load is transferring from the first to second position, a second control element which is energized by the closing of the above-mentioned starting switch and selects one of the two switches making up the position detecting means, and a third control element which operates in response to the motion of the load transferring from the first to second position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a front view of partial longitudinal section of a motor with a clutch used with the device according to the present invention.

FIG. '2 is a block diagram showing a control system.

'FIG. 3 is an electrical circuit diagram showing the control device according to an embodiment of the present invention.

FIG. 4 is a diagram showing a time chart for the device as shown in FIG. 3.

FIG. 5 is a diagram for explaining the relations of the rotational positions of a pedal of an industrial sewing machine.

FIG. 6 is an electrical circuit diagram showing the control device according to another embodiment of the present invention.

FIG. 7 is an electrical circuit diagram showing another embodiment.

FIG. 8 is an electrical circuit diagram showing still another embodiment.

FIG. 9 is an electrical circuit diagram showing still another embodiment.

FIG. 10 is an electrical circuit diagram showing still another embodiment.

FIG. 11 is a front view showing a partial longitudinal section of a most effective operating lever.

FIG. 12 is a diagram showing a section taken in the line XII-XII of FIG. 11.

FIG. 13 is a characteristics diagram showing a working stroke of the operating lever.

FIG. 14 is a partial front view of the operating lever with a safety device operated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a motor with a clutch used as a driving source for an industrial sewing machine, in which a brake is made rotatable so that low-speed rotations are controlled by means of a sub-motor and brake. Numeral 1 shows a motor with a rotor 2 and a stator 3. A shaft 4 of the rotor 2 is mounted rotatably in a housing 7 through bearings 5 and 6 with a flywheel 8 attached to an end thereof to store energy. Numeral 9 shows a friction plate fixed on the side of the flywheel 8, opposite to which a clutch plate 11 is mounted at an end of the clutch shaft 10 which is slidable in the axial direction coaxially with the rotary shaft 4. Further, the clutch shaft 10 is rotatably mounted, through the bearings 14 and 15, on the sliding cylinder 13 which is mounted on the end bracket 12 so as to be slidable in the axial direction. Numeral 16 shows a pulley mounted at the other end of the clutch shaft 10 and coupled with another not-shown pulley on the load shaft by the agency of a belt. Numeral 17 shows a friction plate of a rotary brake 18 opposite to the other side of the flywheel 8 of the clutch plate 11, the brake 18 being mounted rotatably, through the bearing 19, on a projected cylinder 20 of the end bracket 12. A worm gear 21 is provided on a side opposite to the friction plate 17. The worm gear 21 is adapted to engage with a worm which is coupled to the sub motor 22 and sub brake (not shown). An end of the operating lever 23 is supported on the outer periphery of the sliding cylinder which controls the slide of the clutch shaft 10 in the axial direction. The operating lever 23 is rotatably supported, through a pin 25, on a protrusion 24 formed on the bracket 12, and is usually pulled in one direction by a return spring 26 with an end fixed on the bracket 12. The other end 27 of the operating lever 23 is adapted to move downward for operation by means of a control rod (not shown) interlocked with, for example, a pedal of the sewing machine.

In a motor with a clutch with the above-mentioned construction, the rotary shaft 4 rotates integrally with the flywheel 8 when the main motor 1 is connected with a power supply (not shown). Then, an operators pushing down of the end 27 of the operating lever 23 causes the other end of the operating lever 23 to turn with theprotrusion 24 of the housing 12 as a supporting point against the return spring 26, thereby moving the sliding cylinder 13 leftward in the axial direction. As a result, the clutch plate 11 is pressed against the friction plate 9 of the flywheel 8, transmitting the turning effort of the main motor 1 through the friction plate 9, clutch plate 11 and clutch shaft to the pulley 16 to drive the load shaft.

As the operator releases the force applied to an end of the operating lever 23, the operating lever 23 is pulled back by the return spring 26, with the result that the other end of the lever 23 returns the sliding cylinder 13 rightward in the axial direction. The clutch shaft 10 is thus returned to right, and the clutch plate 11 leaves the friction plate 9 of the flywheel 8, being pressed against the friction pate 17 of the brake 18 with the force equivalent to the springiness of the spring 26. In this case, if the worm is driven by the sub-motor 22, the load is driven by the sub-motor 22, through the worm gear 21, friction plate 17 of the brake 18 and the clutch plate 11, at a low speed equivalent to the reduction ratio of the worm. Also, a braking force is transmitted through a like path to the load to stop the same if the-worm gear 21 is braked.

As can be seen from the above description, the motor with a clutch finds use in devices to stop at predetermined positions various loads including sewing machines for industrial use. The operation for controlling such loads will be explained below with reference to a block diagram as shown in FIG. 2. In the figure, numeral 31 shows a main motor, and numeral 32 a brake system which is connected with the load 34 through the clutch 33 with a switching means interposed therebetween. Numeral 35 shows a coupling means for connecting the clutch 33 to the load 34. Numerals 36 and 37 show respectively a sub-motor and sub-brake, one of which can be selectively connected with the brake system 32 through a switching means 38. Numeral 39 shows a load-position-detecting means to detect a regular position of the load 34, and the resulting detection signals are applied to a control means 40 to control the operations of the sub-motor 36 and sub-brake 37. Numeral 41 shows an electrical circuit for controlling the switching means 38 with the output of the control means 40.

In the above-mentioned control system, when the clutch 33 is connected with the main motor by means of the operating lever 23, the torque of the main motor 31 is transmitted to the load 34 to rotate the load 34 at a high speed. Assuming that the switching means 38 is closed on the side of the sub-motor 36, the brake system 32 is driven at a low speed by the submotor 36, and therefore if the force applied by the operating lever 23 is released, the clutch 33 is switched by the return spring 26 from the main motor to the brake system 32. As a consequence, the speed of the load 34 is quickly reduced to a level corresponding to the low speed of the brake system, resulting in a low speed operation supported by the turning effort of the sub motor 36. When the detecting means 39 detects the predetermined position of the load 34 after the load 34 enters a low speed run, the control means 40 is actuated to turn the switching means 38 from the sub motor 36 to the subbrake 37 through the electrical circuit 41, so that the load is stopped quickly and accurately at the predetermined position.

An embodiment of the control device with the abovementioned construction will be explained below with reference to an electrical circuit diagram of FIG. 3.

Numeral 51 shows a power supply which is connected with the primary winding 53 of a reducing transformer 52, the secondary winding 54 thereof being connected with an input terminal of a rectifier 55. An output terminal of the rectifier 55 is connected with a parallel circuit including a resistor 56 and capacitor 57. Numeral 58 shows a coil of the sub-brake 37, which is connected across the rectifier 55 through the transistor 59, the base of the transistor 59 being connected to an output terminal on the positive side of the rectifier 55 through the resistors 60 and 61. Numeral 62 is a coil for a first relay 63, an end of which is connected with the positive side of the rectifier 55, the other end thereof being connected with a base resistor 60 of the transistor 59 through the diode 64. Numeral 66 shows a thyristor which is connected with the power supply 51 through the sub-motor 36, the gate of the thyristor 66 being supplied with a gate signal through the resistor 67 and the contact 63-1a of the relay 63. Numeral 80 shows a relay coil of the relay 81 with an end thereof connected to a positive output terminal of the rectifier through a switch 82, for example, which is disposed under the sewing machine proper and operated by the knee of the operator. The other end of the relay coil 80 is connected with the negative output terminal of the rectifier 55 through a normally-opened contact 81-1a of the second relay 81. Numeral 81-2 shows a second contact of the relay 81, which is connected not only with the base of the transistor 59 through the diode 64 and resistor but with an end of the coil 62 of the first relay 63. The normally-opened contact 81-2a of the relay 81 is connected with a switch 71 which detects a lower position of a sewing needle, while the normally-closed contact 81-2b is connected with a switch 72 for detecting an upper position thereof. Numeral 63-2 shows a second contact of the first relay 63, which is connected with a positive output terminal of the rectifier 55. A normally-opened contact 63-2a of the relay 63 is connected with a terminal of the coil 80 of the second relay 81, while the normally-closed contact 63-2b is connected with the base of transistor 59 through the resistors 61 and 60. Numerals 90 and 91 show diodes respectively inserted between the switch 69 and coil 62 of the first relay 63 and between switch 69 and coil 80 of the relay 81.

In the above-described circuit arrangement, when the switch 69 is opened, no current flows in the coil 62 of the first relay 63, maintaining the normally-opened contact 63-1a in an opened state, and as a result no gate signal is applied to the thyristor 66. The thyristor 66, therefore, is not conducting, which in turn results in no current flowing in the motor 36 connected in series with the thyristor 66. The switch 69 is opened or closed by means of an operating pedal of a load such as an industrial sewing machine. The relations between the operating pedal and the operating lever 23 provided on the motor as shown in FIG. 1 will be explained below with reference to FIG. 5.

In FIG. 5, numeral 27 shows an end of the operating lever 23 which is coupled with the connecting rod 73. Numeral 74 shows an operating pedal of the sewing machine which is sup ported by the pin 75 so as to be rotatable within the range from A to E as shown in the figure. The operating pedal 74 has a connecting rod 76 mounted on an end thereof, which is connected, through a connecting means 77, with the connecting rod 73 which is coupled with the end 27 of the operating lever 23. In a stationary condition where no force is applied to the pedal 74, the pedal 74 is at a position C, while it is changed to position B when it is pushed forward lightly enough not to pull down the end 27 of the operating lever 23. The pedal changes 7 its position further to A when pushed deeper forward. At the pedal position A, the operating lever 23 is pulled down, pressing the clutch plate 11 as shown in FIG. 1 against the friction plate 9, and therefore the sewing machine starts running at a high speed.

On the other hand, the pedal reaches position D at a light backward depression thereof and position E at a stronger depression thereof backward. In this case, as in the forward depression, it is possible to change the position of the pedal 74 without changing the state in which the operating lever 23 is pulled by the return spring 26. The switch 69 is so arranged as to close at the pedal positions A and B and to open at the positions C, D and E. The switches 71 and 72 are provided for the purpose of detecting the position of the load, and are so re lated in operation with the rotary shaft of the sewing machine that the switch 71 is opened only when the load shaft is at a first position, for example, a lower position of the needle, while the switch 72 is opened only at a second position of the load shaft, for example, an upper position of the needle.

At the pedal position A of FIG. 5, the end 27 of the operating lever 23 is pulled downward against the return spring 26 and hence the other end of the operating lever 23 is moved toward left in FIG. 1, thereby moving the sliding cylinder 13, with the result that the clutch plate 11 is pressed against the friction plate 9. As a result, the sewing machine starts a high speed operation by means of the main motor 1, while at the same time the switch 69 is closed, exciting the coil 62 of the first relay 63. Thus the sub-motor 36 is fed through the thyristor 66, driving the motor 36.

Changing the pedal position to B at this time causes the clutch plate 11 to be pressed against the friction plate 17 of the brake 18, so that the sewing machine is quickly reduced in speed to a low-speed state. When the pedal is returned subsequently to position C, the switch 69 is accordingly opened. However, since the normally-opened contacts 8l-1a and 8l-2a of the second relay 81 are both closed, the switch 71 is opened at the lower position of the sewing needle and the coil 62 of the first relay 63 is de-energized, closing the normallyclosed contact 63-212. Then the sub-brake 37 is actuated through the transistor 59 to stop the sewing machine. The second relay 81, which is self-maintained through the switch 82 and normally-opened contact 81-1a, is released from the self-maintenance by temporarily opening the switch 82, and the contact 81-2 is switched back to the normally-closed side 81-2b. As a result, the first relay 63 is again excited to drive the motor 36, and the sewing machine is slightly moved to switch the needle from the lower to upper position, opening the switch 72 and stopping the sewing machine at the upper position. Unless the switch 69 is closed again, the sewing machine does not start, holding the needle at the upper position even if the pedal 74 is pressed to position C, D or E.

As will be understood from the above description, the device according to the present invention is very effective in that great safety of the operator is assured because the switch system including the position-detecting switches 71 and 72 which the operator is most liable to touch is reduced in voltage by means of the transformer 52 and the first relay 63. Further, since the coil 58 of the brake 37 is controlled through the transistor 60 and the base current of the transistor 60 is controlled simultaneously with the position detection, time lag is eliminated in a braking operation, making possible accurate and immediate response.

Another embodiment of the invention which has the function similar to that of the embodiment shown in FIG. 3 is illustrated in FIG. 6. (Those component elements which are marked with the same numerals as in FIG. 3 work similarly and detailed description of them will be partially omitted.) Numeral 80 shows a relay coil of the relay 81 with a terminal thereof connected through the diode 95 to a positive output terminal of the rectifying means 55, the other terminal thereof being connected with a negative output terminal of the rectifying means 55 through the diode 91 and switch 69. Numeral 96 shows a resistor connected in series with a capacitor 97 and in parallel with the relay coil 80 of the relay 81. The second relay 81 has the normally-opened contact 8l-la, normally-closed contact 81-3b and switching contact 81-2. A terminal of the normally-opened contact 81-1a is connected, through the diode 91, to the switch 69 and also to thecoil 80 of the relay 81, the other terminal thereof being connected with the negative-pole side of the rectifying means 55 through the lowerr position detecting switch 71. On the other hand, a terminal of the normally-closed contact 99 is connected with the positive terminal of the rectifying means 55 through the coil 102 of the relay 101, while the other terminal thereof is connected to the upper-position detecting switch 72 through the knee switch 82 provided on the sewing machine. Numeral 81-2a shows a normally-opened contact opposed to the switching contact 100 of the second relay 81 and, like the normally-opened contact 81-1a, connected to the lower-position detecting switch 71. The normally-opened contact 81-2b is connected, through the normally-opened contact 101-la of the third relay 101, to the upper-position detecting switch 72, and also with a terminal of the third relay coil 102 through the diode 106. The switching contact 8l-2 of the second relay 81 is connected with a terminal of the coil 62 of the first relay 61 through the diode 107, and also with the base of the transistor 59 through the diode 107, diode 64 and the base resistor 60.

In the above-mentioned circuit arrangement, depressing the pedal 74 (to position A or B) closes the switch 69. Then the first relay 63 and second relay 81 are energized to start the sub-motor 36, while at the same time closing the contacts 81-1a and 81-2a and opening the contacts 8l-3b and 81-2b.

When the pedal 74 is returned to the stationary position (C), the interlocked switch 69 is accordingly opened. How ever, since the normally-opened contacts 81-la and 81-2a of the second relay 81 are self-maintained by the relay coil 80, the sub-motor 36 continues running until the sewing needle reached the lower position, energizing the lower-position detecting switch 71.

When the lower-position detecting switch 71 is opened, the first relay 63 is de-energized and thereby the sub-motor 36 is stopped, but the second relay 81 is kept closed by means of the capacitor 97 and resistor 96 in parallel with the second relay coil until the speed of the sewing machine is reduced gradually to the point where it can be stopped accurately enough by the sub-brake 37.

After the sewing needle is stopped at the lower position and the switch 71 and the second relay 81 are opened to close the normally-closed contacts 8l-3b and 81-2b, the operator's closing the knee switch 82 causes the relay coil 102 of the third relay 101 to be energized through the normally-closed contact 81-3b, knee switch 82 and upper-position detecting switch 72, and the normally-opened contact 101-1a is closed, thereby exciting again the relay coil 62 of the first relay 63. As a result, the sub-motor 36 continues to be driven until the sewing needle reaches the upper position and the detecting switch 72 is opened. In this case, the diode 106 is adapted to selfmaintain the relay 101 in spite of the operation of the knee switch 82 by the operator to energize the coil 102 of the third relay 101.

It will be understood from the above description that the second relay 81 and knee switch 82 employed in the present invention make possible an electrically-maintained system, contributing to a further simplification of the operations, so that not only even unskilled workers can handle the sewing machine but the control device can be applied to various other controlling operations.

FIG. 7 illustrates another embodiment which is an improvement on the device of FIG. 6 to be applied to various controls of the sewing machine. In FIG. 7, those component elements with the same numerals as in FIGS. 3 and 6 function similarly and will not be described in detail. Numeral 110 shows a main coil of the sub-motor 36 which is connected to the power supply 51 through the thyristor 66. Numeral 111 shows an auxiliary coil of the sub-motor 36 which is connected in series with the capacitor 112 and in parallel with the main coil 110 through the switching contact 1012 interlocked with the normally-opened contact 101-1a of the kind relay 101. A terminal of the relay coil 102 of the third relay 101 is connected to a positive output terminal of the rectifying means 55 through the diode 114, while the other terminal thereof is connected to the knee switch 82 through the normally-closed contact 81-3b of the second relay 81 and the thyristor 11S and also to the upper-position detecting switch 72 through the diode 106 and the normally-opened contact 101-1a of the third relay 101. The gate of the thyristor 115 connected in series with the third relay coil 102 is connected not only with the positive terminal of the rectifying means 55 through the resistor 116 but also with the negative terminal of the rectifying means 55 through the lower-position detecting means 71 and diode 117. Numeral 118 shows a capacitor of a delay circuit connected in series with the resistor 119, and the series circuit including the capacitor 118 and resistor 119 is connected in parallel with the relay coil 102 of the third relay coil 101.

In the above-described circuit arrangement, the closing of the switch 69 interlocked with the pedal 74 energizes the first relay 63 and second relay 81, rotating the sub-motor 36 in the forward direction, and the contacts 81-1a and 81-2a are closed, while the contacts 81-3b and 81-2b are opened.

When the pedal 74 is returned to the stationary position (position C in FIG. the interlocked switch 69 is opened, but since the normally-opened contacts 81-1a and 81-2a of the second relay 81 are self-maintained in a closed state, the submotor 35 continues running in the forward direction until the sewing needle reaches the lower position. When the needle reaches the lower position, the detecting switch 71 is opened to cut off the power to the sub-motor 36.

After the sewing needle stops at the lower position, the relay coil 80 of the second relay 81 is de-energized and the normally-closed contacts 81-2b and 81-3b are closed. Then, closing the knee switch 82 causes a gate signal to be applied to the gate of thyristor 115 through the resistor 116, energizing the thyristor 115. As a result, the relay coil 102 of the third relay 101 is excited, closing the normally-opened contact 101-1a, while at the same time energizing the switching contact 101-2 of the interlocked sub-motor 36 thereby to reverse the connection of the auxiliary coil 111. Consequently, the first relay 63 is energized again through the normally-opened contact 101-1a and the contact 63-1a is closed to feed the sub-motor 36 again through the thyristor 66. Thesub-motor 36 is thus reversed in rotation, and when the sewing needle reaches the upper position, the switch 72 is opened to stop the sewing machine.

The thyristor 115 which has the resistor 116 and diode 117 in its gate circuit is energized only at the lower position of the sewing needle when the lower-position detecting switch 71 is opened, and thereby the relay coil 102 of the third relay 101 is excited. The thyristor 115 thus prevents the sewing machine from rotating in the reverse direction at a given position of the sewing needle.

According tothe present invention embodied'as above, the switching of the sub-motor 36 between forward and reverse rotations can be conducted by means of the switching contact 101-2, which is controlled by the third relay 101, without any current flowing in the contact 101-2. In addition, since the sub-motor starts running in the reverse direction only after the sewing needle stops at a predetermined position, no damage to the device is caused due to mishandling of it.

FIG. 8 illustrates another embodiment of the invention provided with an automatic thread-cutting means. In the figure, like reference numerals indicate like components in FIGS. 3 to 7 and will not be described in detail. Numeral 120 shows a solenoid for a thread-cutting knife with an end thereof, like an end of the third relay coil 102, connected with the positive output terminal of the rectifying means 55, the other end thereof being connected to the rectifying means 55 through the normally-opened contact 101-3a interlocked with the normally-opened contact 105 and the third switch 122 for detecting the needle position. Numeral 123 shows a wiper solenoid to remove the upper portion of the thread after cutting it off,

, and 101-3a of the third relay 101. A terminal of the capacitor 126 is connected to the positive side of the rectifying means 55 through the normally-opened contact 10140, resistor 128 and diode 129, while the other terminal thereof is connected with the negative side of the rectifying means 55.

In the above-described circuit arrangement,- when the pedal 74 is returned to the stop position from the high or low speed operation in which the switch 69 interlocked with the pedal 74 is closed and the first relay 63 and second relay 81 are energized to drive the sub-motor 36, the interlocked switch 69 is opened, so that when the sewing needle reaches the lower position, the detecting switch 71 is actuated and the submotor 36 is stopped being fed, thereby stopping the sewing needle at the lower position. Then, the second relay 81 is deenergized, closing the normally-closed contact 81-2b. The closing of the switch 82 causes the relay coil 102 of the third relay 101 to be excited and thereby the normally-opened contacts 101-1a, 101-3a and 1014a are closed. As a result, the capacitor 126 begins to be charged through the resistor 128,

while at the same time exciting the coil 62 of the first relay 63,

and so the sub-motor 36 is again started through the thyristor 66 thereby to start moving the sewing needle from the lower to upper position.

At a point slightly up from the lower needle position, the third switch 122 for position detection is closed to energize the solenoid for operating the thread-cutting knife. (not shown in the drawing) The needle continues moving upward and stops at the upper position. It is possible to de-energize the solenoid 120 to return the knife to the original position before the needle stops at the upper position, depending on the time at which the third switch 122 for position detection is closed.

When the sewing needle reaches the upper position and the position-detecting switch 72 is opened, the relay coil 62 of the first relay 63 and relay coil 102 of the third relay 101 are deenergized, so that the sub brake is actuated not only to stop the sewing machine but to open the normally-closed contact 101-3a. As a result, the solenoid 180 is de-energized and the change-over switch l01-4 transfers from normally-opened contact 101-4a to normally-closed contact 101-4b, whereby the electric charges in the capacitor 126 is discharged in a short time through the wiper solenoid 123, which in turn causes the wiper to be driven by the wiper solenoid 123 to remove the upper portion of the thread cut off. The thyristor 115 is constructed, as in FIG. 7, such that the third relay 101 is started to be energized only when the sewing needle is stopped at the lower position. I

As can be seen from above, not only the control of the thread-cutting knife and thread-removing wiper is simplified, but also the returning of the thread-cutting knife to the original position can be adjusted by means of the third switch for position detection. In addition, the operating safety and accuracy are assured by the thyristor.

Still another embodiment of the invention is shown in FIG. 9, in which like numerals indicate like components in FIGS. 3 to 8 and will not be explained in detail. A terminal of the relay coil 102 of the relay 101 is connected with a positive output terminal of the rectifying means 55, the other terminal thereof being connected with the upper-position detecting switch 72 through the thyristor 115, normally-closed contact 81-3b of the second relay 81, contact 63-3b of the first relay 63 and switch 131 which is interlocked with the position of the pedal 74. The other terminal of the relay coil 102 is also connected with the above-mentioned detecting switch 72 through the diode 106 and the normally-opened contact 101-1a of the third relay 101. The zener diode 132 which is connected to the gate of the thyristor 115 is further connected not only with the positive terminal of the rectifying means 55 through the resistor 116 but also with the normally-closed contact 81-3b of the second relay 81 through the capacitor 133 and diode 134. The zener diode 132 is also connected to the lower-position detecting switch 71 through the diode 117. Numeral 135 shows a diode for blocking the reverse current with a terminal thereof connected with a terminal of the capacitor 133, the other terminal of the diode 135 being connected to the negative side of the rectifying means 55. Numeral 136 shows a solenoid for a safety means which is connected in parallel with a series circuit comprising the resistor 137 and capacitor 138. A terminal of the solenoid 136 is connected to the positive side of the rectifying means 55 through the diode 139, the other terminal thereof being connected not only to the contact 63-312 of the first relay 63 through the diode 140 but also with the negative side of the rectifying means 55 through the switch 141 which is kept closed while the wiper is being operated by the wiper solenoid 123. A terminal of the solenoid 120 to operate the thread-cutting knife is connected to the positive terminal of the rectifying means 55, and the other termianl thereof not only with the negative terminal of the rectifying means 55 through the normally-opened contact 101-3a of the third relay 101 but also with a terminal of the solenoid 136 of the safety means through the diode 142. Numeral 143 shows a switch which operates in response to the movement of pedal 74 to the respective positions, and its movable contact 144 is connected to the diode 107 through the normally-opened contact 81-2a of the second relay 81. The contact 143-a opposed to the movable contact 144 is connected not only with the lower-position detecting switch 71 but also with the second relay coil 80 through the normally-opened contact 81-1a of the second relay 81, while the contact 143-b is connected with the upper-position detecting switch 72.

The contact 143-a of the switch 143 is closed at the positions D and E of the pedal 74 as shown in FIG. 5, and the contact 143-b thereof is closed at the pedal positions A, B and C.

In the above-described construction of the control device according to the present invention, the sewing machine runs at a high speed at position A of the pedal 74 and runs at a low speed at position B. When the pedal 74 is at position C or D, the sewing needle stops at the upper and lower needle positions respectively. At the pedal position E, the sewing needle automatically moves from lower up to upper position after temporarily stopping at the lower positions, while the threadcutting knife works.

In other words, at the pedal positions A and B, the interlocked switch 69 is closed and thereby the first relay 63 is energized to rotate the sub motor 36'. When the switch 69 is opened (at the pedal position C), the relay coil 80 of the second relay 81 is kept excited due to its self-maintaining function, and accordingly the relay coil 62 of the first relay 63 is excited through the normally-opened contact 81-2a of the second relay 81, contact 143-b of the switch 143 which operates in response to each position of the pedal 74, and the upper-position detecting switch .72. Thus, the sewing needle reaches the upper position, the switch 72 is opened, the first relay 63 is de-energized, and the sewing machine is stopped.

Under this condition, changing the pedal position to D causes the contact l43b of switch 143 to be opened, closing the contact 143a, so that the sewing needle is driven by the sub motor 36 until it reaches the lower position, The sewing needle stops when the lower-position detecting switch 71 is opened. As a result, the relay coil 80 of the second relay 81 is de-energized and the normally-opened contact 81-2a is opened, while the normally-closed contact 81-2b is closed.

Changing the position of pedal 74 to E causes the interlocked switch 131 to be closed, so that the solenoid 136 for the safety means is excited through the contact 63-3b, switch 131 and upper-position detecting switch 72. The safety means which is disposed near the pedal 74 is provided for the purpose of mechanically preventing the pedal 74 from changing its position to A or B when the solenoid 136 is excited, in order that the sewing machine may not be operated at a high speed when the thread-cutting knife is working.

The contact 81-3b is a normally-closed contact for the relay 83. Although the thyristor 115 operates in the manner mentioned above, it begins conducting when the charging voltage of the capacitor 133 which begins to be charged after the closing of switch 131 reaches the operating voltage of the zener diode 132, because the zener diode 132 and capacitor 133 are connected with the gate circuit of the thyristor 115. Then the solenoid 136 for the safety means is excited for the complete restraint of the pedal 74 by the safety means, followed by the excitation of the relay coil 102 of the third relay 101. When the contacts 101-1a, 101-3a and 101-4a are closed after excitation of the relay coil 102 of the relay 101 due to the conduction of the thyristor 115, the sewing needle moves to the upper position while the solenoid 120 for the thread-cutting knife is excited. In this case, as long as the contact 101-3a is kept closed by means of the diode 142, the safety means continues working even if the pedal 74 changes its position from E to D or C. When the sewing needle reaches the upper position and the position-detecting switch 72 is opened, the first relay 63 and third relay 101 are both tie-energized, actuating the sub brake 37, and thereby the sewing machine is stopped. As a result, the contact 101-311 is opened and the switching contact 101-4 switches from the normally-opened contact 101-4a to the normally-closed contact 101-4b, so that the charges of the capacitor 126 which was stored earlier through the resistor 128 are discharged in a short time through the wiper solenoid 123, with the result that the wiper is driven by the wiper solenoid 123 thereby to remove the upper portion of the thread cut off. In this case, the resistor 137 and capacitor 138 operate such that the solenoid 136 for the safety means continues to be excited until the switch 141 which operates in response to the wiper is closed even after the third relay 101 is de-energized.

As will be understood from the above description, according to the present invention, provision of the switch 143 which operates in concert with the pedal 74 makes it possible to stop the sewing machine at the second (upper) position without operating the thread-cutting knife. Also, the sewing needle can be held in position by means of an electrical circuit even if the switches without any function of maintenance are employed. Further, when the thread-cutting knife is instructed to operate, the movement of pedal 74 is quickly limited, thereby completely protecting the sewing machine from damage due to its mishandling.

Still another embodiment is shown in FIG. 10 in which like numerals indicate like component elements in FIGS. 3 to 9 and therefore detailed description of them will be omitted. Numeral 150 shows a thyristor connected in series with the solenoid for the thread-cutting knife. The cathode of the thyristor is connected with the negative output terminal of the rectifying means 55, while the anode thereof is connected not only to the positive terminal of the rectifying means 55 through the solenoid 120 but also to the positive terminal of the rectifying means 55 through the diode 142 and solenoid 136 for the safety means. The gate of the thyristor 150 is connected with its cathode through the resistor 151, normallyopened contact 101-5a of the third relay 101 and capacitor 154. A terminal of the solenoid 136 for the safety means is connected with the positive terminal of the rectifying means 55, while the other terminal thereof is connected not only with the negative terminal of the rectifying means 55 through the switch 141 which is kept closed during the operation of the wiper, but also with the upper-position detecting switch 72 through the diode 140, normally-closed contact 63-3b of the first relay 63 and switch 131 which operates in response to each position of the pedal 74. A terminal of the relay coil 102 of the third relay 101 is connected with the positive side of the rectifying means 55, while the other terminal thereof is connected not only with the contact 63-3b of the first relay 63 through the normally-closed contact 8l-3b of the second relay 81 but also with the upper-position detecting switch 72 through the diode 106 and the normally-opened contact 101-1a of the third relay 101. Numeral shows a diode with a terminal thereof connected with a terminal of capacitor 154, the cathode side of the diode 155 being connected with the negative side of the rectifying means 55 through the lowerposition detecting switch 71. Numeral 156 shows a resistor with a terminal thereof connected with the positive side of the rectifying means 55, the other terminal thereof being connected with the capacitor 154 through the normally-closed contact 101-5b of the third relay 101. Numeral 158 shows a capacitor with a terminal thereof connected with the anode of the thyristor 150, the other terminal thereof being connected with the gate of the thyristor 150 through the normallyopened contact 101-5a of the switching contact 101-5 and resistor 152.

In the above-described circuit arrangement according to the present invention, pushing the pedal 74 to position A or B causes the interlocked switch 69 to be closed, and the first relay 63 is energized thereby to start the sub-motor 36. At the pedal position C, opening of the switch 69 causes the relay coil 62 of the first relay 63 to be excited through the normallyopened contact 81-2a of the second relay 81 and contact 143-b of the switch 143 because the relay coil 80 of the second relay 81 is self-maintained in an excited state through the contact 8l-1a and the lower-position detecting switch 71. Therefore, when the sewing needle reaches the upper position, the switch 72 is opened and power supply to the first relay 63 is cutoff, thereby stopping the sewing machine.

At this time, by changing the pedal position to D, the contact 143-b of the switch 143 is opened and thereby the contact 143-a is closed, so that the sewing needle is driven to the lower position by the sub-motor 36 and stops as the lowerposition detecting switch 71 is opened. When the switch 71 is opened, the relay coil 80 of the second relay 81 is de-energized and thereby the normally-opened contact 81-241 is opened, while the normally-closed contact 81-2b is closed.

Pushing the pedal 74 further to position E, the switch 131 interlocked with the pedal 74 is closed to excite the solenoid 136 for the safety means through the contact 63-3b, switch 131 and upper-position detecting switch 72.

In a condition where the third relay 101 is not energized, that is, when the sewing needle is at the lower position, the capacitor 154 is charged through the resistor 156, normallyclosed contact 101-512 of the third relay 101, and when the normally-opened contact 101-5a of the switch 101-5 is closed by the excitation of the relay coil 102 of the third relay 101, the electric charges in the capacitor 154 flows to the gate of the thyristor 150 through the resistor 151. The resultant conduction of the thyristor 150 is followed by the excitation of the solenoid 120 for the thread-cutting knife and the charging of the capacitor 158. When the sewing needle transfers to the upper position and the third relay 101 is opened, the electric charges of the capacitor 158 are applied as a reverse voltage between anode and cathode of the thyristor 150 through the contact 101-5b, diode 155 and position-detecting switch 71, thereby cutting off the thyristor 150.

The above-described construction of the present invention makes possible a contactless switching system by the use of a thyristor to control the solenoid for the thread-cutting knife which is easy to be broken. This not only results in a longer life of the device but makes it possible to control various components including the knife, wiper and safety means.

The most effective of the operating lever 74 provided with such control means with various possibilities will be explained below with reference to FIG. 11. In this figure, the operating lever 23 is rotatably supported on the protrusion 24 of the end bracket 12 through the pin 25, and usually pulled in one direction by the return spring 26 with an end thereof fixed on the other protrusion 201 formed on the bracket 12. Numeral 202 shows a bar for supporting the return spring 26 through the washer 203 and nut 204. The operating lever 23 comprises a main body 205 with an end thereof engaged with the sliding cylinder 13 and an auxiliary portion 206 with an end thereof rotatably mounted on the main body 205 through the pin 207. The auxiliary portion 206 has a protrusion 208 with an aperture with which the connecting rod 73 of the pedal 74 engages, while the hook 210 is provided at the other end of the auxiliary portion 206. On the other hand, numeral 211 shows a plate which is fastened to the main body 205 with a screw or the like, and a movable plate 212 is mounted slidably on the plate 211, while the safety means 214 is fixed thereon through the support metal 218. The supporting plate 219 interlocked with the movable plate 212 is mounted on the edge of the plunger of the safety means 214 through the pin 217, the movable plate 212 being usually engaged with the hook 210 on the edge of the auxiliary portion 206 by means of the spring 216. In other words, when the solenoid 136 of the safety means 214 is excited, the plunger 215 is attracted leftward in the drawing and the interlocked movable plate 212 accordingly moves, whereby the hook 210 is disengaged with the edge of the auxiliary portion 206 so as to be movable freely downward.

On the other hand, the upward movement of the hook 210 is limited by the adjustable stopper 220 provided on the main body 205 of the lever, and when the solenoid 136 of the safety means 214 is de-energized, the movable plate 212 engages with the hook 210, which rotates together with the main body 205 with the pin as a supporting point.

Numeral 222 shows a first spring provided between the main body 205 and auxiliary portion 206 of the operating lever 23 to act to bring the main body 205 near to the auxiliary portion 206. For this purpose, the first spring 222 is adjustable with the bolt 223, washer 225 and nut 224. Numerals 226 and 232 show second and third springs respectively mounted in parallel with each other in such a manner that the main body 205 and auxiliary portion 206 are separated from each other. The springiness of the first spring 226 is adjustable by means of the bolt 227, washer 228 and nut 229, while the third spring 232 is mounted between the main body 205 and auxiliary portion 206 by means of the bolt 233, washer 231 and nut 234. Numeral 230 shows a space which is provided between an edge of the spring 232 and auxiliary portion 206 so that the third spring 232 operates after the auxiliary portion 206 has moved a certain distance upward. Numeral 143 shows a first switch which is provided between main body 205 and auxiliary portion 206 so as to operate by the amount corresponding to the relative motion of the auxiliary portion 206 against the main body 205, and the switch 143 is mounted on the wall of the main body 205 of the lever through the screw 239 as shown in FIG. 12, the movable portion 236 of the switch 143 being operated by the first actuator 237 which is mounted on the auxiliary portion 206 through the screw 238. Numeral 131 shows a second switch which is mounted on the wall of the main body 205 on the side opposite to the first switch 143 through the screw 241, and the movable portion 245 is disposed opposite to the second actuator 242 which is fixed, through the screw 243, on the auxiliary portion 206.

On the other hand, the third switch 69 is fixed on the wall 248, which occupies a part of the lever auxiliary portion 206, through the screw 247, the movable portion 249 of the switch 246 being engaged with the movable plate 212. Further, numeral 250 shows a rod with an end hook 255 fixed on the protrusion 256 formed on the bracket 12. The rod 250 passes through a hole 254 of the main body 205 and a hole 253 of the auxiliary portion 206, and, on an end thereof, has an adjustable nut 251 and washer 252.

Because of the above-described construction, when the safety means 214 is energized, the movable plate 212 moves leftward in FIG. 11, making the hook 210 of the lever auxiliary portion 206 ready for free downward movement. Thus, when pulled down by means of the connecting rod 73 engaged with the aperture 209 in the protrusion 208 of the auxiliary portion 206, the auxiliary portion 206 moves downward a certain distance and is stopped by the washer 252 provided therethrough.

The operation of the operating lever 23' in the abovedescribed construction will be explained below. Pushing down the pedal 74 to position D of FIG. 5 causes the second spring 226 to be contracted. Then the first switch 143 is energized by the actuator 237. Further, pushing down backward the pedal 74 to position E of FIG. 5, the third spring 232 is also contracted thereby to energize the second switch 131 through the actuator 242. The pedal 74 does not move upward any more even if it is depressed, because the hook 210 of the auxiliary portion 206 contacts and is stopped by, the bottom of the bolt 220 fixed on the main body 205. The relations among the above-mentioned operations will be explained with reference to the characteristics diagram of FIG. 13. The line from point III to point IV shows the contracting stroke of the second spring 226, the first switch 143 being energized at an intermediate point Y. The line from point IV to point V indicates a stroke in which the third spring 232 is also contracted, the second switch 131 being energized at an intermediate point 2. Similarly, when the pedal 74 depressed forward to position A or B of FIG. 5, the connecting rod 73 pulls down, as shown in FIG. 11, the auxiliary portion 206 thereby to contract the first spring 222. The stroke in this case is shown by the line between points III and II of FIG. 13, within the range of which the switch 69 is energized at point X because the actuator 249 of the third switch 69 is restricted in operation by the movable plate 212. Then the hook 210 of the auxiliary portion 206 comes into contact with the movable plate 212 and contracting the return spring 26 of the lever 23 together with the main body 205, moves the sliding cylinder 13 leftward as shown in FIG. 1, so that the torque of the main motor 1 is transmitted to the pulley 16 through the clutch plate 11.

The safety means 241 operates not in the manner that the pedal 74 is prevented from moving to position A or B of FIG. while the thread-cutting knife is in operation, but only in the manner that the auxiliary portion 206 is moved down in FIG. 11 according as the pedal 74 is pushed forward. In other words, when the solenoid 136 of the safety means 214 is excited, the movable plate 212 is pulled leftward as shown in FIG. 14 and therefore both the hook 210 of the auxiliary por" tion 206 and movable portion 249 of the switch 240 are made free and drop.

As can be seen from above, the present invention simplifies the multi-purpose control device because a safety means to cope with the case of mishandling is integrated with switches. In addition, free stroke is allowed to the operating lever 23 without affecting the other sequences, thereby eliminating the need for complementary means and assuring accurate operations of the safety means. Further, in controlling a load by means of a motor with a clutch, compensation for the wear of the clutch can be performed merely by correcting the clutch itself while maintaining the accompanying switch system at a regular position.

We claim:

1. A motor-controlling device comprising a position-detecting means including two switches which operate respectively at first and second positions of a load driven by a motor, a first control element which is energized through a starting switch closed in starting a job and closes a driving circuit for said motor while said load moves from said first position to second position, a second control element which is energized by closing said starting switch and selects one of said two switches for said position-detecting means, and a third control element which operates in response to the movement of said load from said first position to said second position.

2. A motor-controlling device according to claim 1, in which said first and second control elements comprise first and second relays respectively, and said third control element is inserted in a self-maintenance circuit for said second relay and comprises an instruction switch for energizing the second relay to move the load from said first position to said second position.

3. A motor-controlling device according to claim 1, in which said first and second control elements comprise first and second relays respectively, and the third control element is controlled by an instruction switch for instructing the load to move from said first position to said second position and by the position-detecting means, said third control element comprising a third relay for controlling the forward and reverse rotations of the motor.

4. A motor-controlling device according to claim 1, in which said third control element further comprises a means for driving a knife and wiper.

5. A motor-controlling device according to claim 4, in which excitation of the third control element is controlled through an instruction switch for instructing the load to move from said first position to said second position and through the position-detecting means, said third control element comprising a third relay for controlling a circuit which energizes a solenoid to drive the knife and wiper.

6. A motor-controlling device according to claim 4, in which said third control element comprises a third relay whose excitation is controlled through a switch for instructing the load to move, a thyristor which is controlled through a switch for detecting the first load position and through a contact of the third relay and connected to a circuit for energizing a solenoid for the knife, and a capacitor whose charging operation is controlled through the contact of said third relay and which controls the conduction of said thyristor.

7. A motor-controlling device according to claim 1, in which said third control element further comprises a safety means for limiting the movement of the load.

8. A motor-controlling device according to claim 7, in which said third control element is inserted between the second control element including a second relay and a switch for the position;detecting means, said third control element comprising a switch operated according to load positions and a third relay which is excited by a switch for instructing the load to move from first to second position and by the positiondetecting means, said third relay controlling a circuit for energizing a solenoid for a safety means which limits the movement of the load.

9. A motor-controlling device according to claim 1, comprising an operating lever for a clutch system capable of a free stroke without giving any electrical signal to any of the control elements, in addition to and in the same direction as a regular stroke for coupling a load shaft with a driving shaft of the motor which is interposed between said two shafts.

10. A motor-controlling device according to claim 9, in which an operating lever for a clutch system added to the motor has a first stroke for mechanically coupling a driving shaft of said motor to a load shaft, a second stroke for instructing the load shaft and driving shaft to be coupled with each other, and a third stroke for stopping the load.

11. A motor-controlling device according to claim 10, in which said motor is provided with an operating lever for a clutch system with a plurality of continuously variable strokes with independently adjustable lengths and operational forces. 

1. A motor-controlling device comprising a position-detecting means including two switches which operate respectively at first and second positions of a load driven by a motor, a first control element which is energized through a starting switch closed in starting a job and closes a driving circuit for said motor while said load moves from said first position to second position, a second control element which is energized by closing said starting switch and selects one of said two switches for said position-detecting means, and a third control element which operates in response to the movement of said load from said first position to said second position.
 2. A motor-controlling device according to claim 1, in which said first and second control elements comprise first and second relays respectively, and said third control element is inserted in a self-maintenance circuit for said second relay and comprises an instruction switch for energizing the second relay to move the load from said first position to said second position.
 3. A motor-controlling device according to claim 1, in which said first and second control elements comprise first and second relays respectively, and the third control element is controlled by an instruction switch for instructing the load to move from said first position to said second position and by the position-detecting means, said third control element comprising a third relay for controlling the forward and reverse rotations of the motor.
 4. A motor-controlling device according to claim 1, in which said third control element further comprises a means for driving a knife and wiper.
 5. A motor-controlling device according to claim 4, in which excitation of the third control element is controlled through an instruction switch for instructing the load to move from said first position to said second position and through the position-detecting means, said third control element comprising a third relay for controlling a circuit which energizes a solenoid to drive the knife and wiper.
 6. A motor-controlling device according to claim 4, in which said third control element comprises a third relay whose excitation is controlled through a switch for instructing the load to move, a thyristor which is controlled through a switch for detecting the first load position and through a contact of the third relay and connected to a circuit for energizing a solenoid for the knife, and a capacitor whose charging operation is controlled through the contact of said third relay and which controls the conduction of said thyristor.
 7. A motor-controlling device according to claim 1, in which said third control element further comprises a safety means for limiting the movement of the load.
 8. A motor-controlling device according to claim 7, in which said third control element is inserted between the second control element including a second relay and a switch for the position-detecting means, said third control element comprising a switch operated according to load positions and a third relay which is excited by a switch for instructing the load to move from first to second position and by the position-detecting means, said third relay controlling a circuit for energizing a solenoid for a safety means which limits the movement of the load.
 9. A motor-controlling device according to claim 1, comprising an operating lever for a clutch system capable of a free stroke without giving any electrical signal to any of the control elements, in addition to and in the same direction as a regular stroke for coupling a load shaft with a driving shaft of the motor which is interposed between said two shafts.
 10. A motor-controlling device according to claim 9, in which an operating lever for a clutch system added to the motor has a first stroke for mechanically coupling a driving shaft of said motor to a load shaft, a second stroke for instructing the load shaft and driving shaft to be coupled with each other, and a third stroke for stopping the load.
 11. A motor-controlling device according to claim 10, in which said motor is provided with an operating lever for a clutch system with a plurality of continuously variable strokes with independently adjustable lengths and operational forces. 